Regarding the perch, perhaps you could remove all the perches so she has to sit on the floor and then put her food and water bowls on the floor. But raise the floor high enough so she can see outside her cage.
Regarding the choice whether to euthanize or treat, I agree with Ericka that's a personal decision.
Regarding your vet's recommended course of testing, that's consistent with how my avian vet has diagnosed my lame budgies. Unfortunately, however, quite often, the first "regular" x-ray was not clear enough to sufficiently pinpoint the problem. But with my last lame budgie, my vet recommended an ultrasound in lieu of the barium series; IIRC, the ultrasound would have been faster and clearer and less expensive. Perhaps you could ask your vet to confer with my vet, who's in Southern California. Here's his website: http://thebirdclinic.com/
. (He'll be back in the office this Friday.) But once your vet does the ultrasound or barium series, she should be able to determine whether surgery or other treatment will be worthwhile.
FWIW, my budgie hen has had liver disease for 3-4 years, but her liver has improved with daily liquid Calorad supplementation and a special liver formulation of Roudybush pellets.
Also, a few of my budgies have had tumors. Despite excellent care, one budgie with a testicle tumor died during surgery (a vein tore) and another with a testicle tumor died after surgery (from previously existing renal failure, not from the surgery).
So in short, even with the best avian veterinary care, you are never guaranteed a successful outcome.